Some modern vehicles, particularly “off-road” vehicles, are adapted to enable the vehicle to wade through flowing water up to a certain depth. Such vehicles are able to safely traverse streams and shallow rivers, without risk of damage to components of the vehicle.
This is of clear benefit in the context of off-road driving, as there is no need for a driver to make route adjustments in order to avoid water. Even in the context of on-road driving, during times of severe flooding a road may have water flowing across it, for example if a nearby river is overflowing. Vehicles adapted for wading through flowing water are more able to cope with this scenario.
To help a driver maintain control of a vehicle while it passes through water, a wading mode may be implemented in which various settings are optimised for wading. For example, steering systems, traction control systems and braking systems may be adjusted to provide a response that is tailored for the purpose of wading.
At present, some known systems enable the vehicle to automatically detect when it is in water, and to activate a wading mode. This provides a convenient arrangement for the driver, who does not need to manually select the wading mode prior to entering the water.
In one example which is described in the Applicant's earlier application WO 2012/080439 A1, a vehicle is provided with acoustic sensors which generate an alert when immersed in water. Generation of the alert is based on the principle that a diaphragm of the sensor settles more quickly when immersed in water than in air. The sensors are positioned at suitable points on the exterior of the vehicle, for example on the underside of a body of the vehicle, at a pre-determined height above the ground. Accordingly, when the sensors generate an alert indicating that they are immersed in water, the water level around the vehicle can be determined by virtue of the known elevation of the sensor. In order to prevent nuisance triggering of the alert, the sensors are placed at a suitable height to ensure that, for example, they do not become immersed as the vehicle drives through puddles.
While this arrangement provides automatic detection of a wading event and automatic activation of a wading mode, this only occurs once the vehicle is immersed in the water to a significant depth. Therefore, there is still potential for reduced control of the vehicle during a period defined between entry into the water and automatic activation of the wading mode.
In a similar arrangement which is described in another of the Applicant's earlier applications, WO 2012/123555 A1, downwardly-directed acoustic sensors are positioned at a known elevation above ground-level and are arranged to emit an ultrasonic signal, and then to detect a reflected signal returning from a surface below. The time-of-flight (TOF) of the signal is determined, from which the distance from the sensor to the surface can be determined using conventional algorithms. If the vehicle is in water, the surface of the water is closer to the acoustic sensor than the surface of the road. As a consequence, when the signal is reflected from the surface of the water, the TOF is shorter than expected. The difference between the expected TOF and the indicated TOF can be used to determine the distance between the sensor and the surface of the water, and therefore the depth of water. This means that the arrangement can determine that the vehicle is in water prior to the acoustic sensors becoming immersed.
The arrangement of WO 2012/123555 A1 can be used as an alternative or in combination with the arrangement of WO 2012/080439 A1 in which sensors generate an alert when immersed, as measurement of the TOF enables earlier detection of a wading situation and thus earlier activation of the wading mode. By improving the responsiveness of the system in this way, the period between entry of the vehicle into water and activation of the wading mode is reduced. However, the immersion sensors as described in WO 2012/080439 may be able to give a more positive determination of a wading event. These systems benefit the driver, as the vehicle can be configured in the correct driving mode, thus providing a tailored response profile, for a higher proportion of driving time, i.e. including when the vehicle is wading.
While both of the above described arrangements can automatically detect entry of a vehicle into water, neither has the capability to determine the water conditions. Different water conditions present different challenges for the vehicle, and so there is potential to tailor the wading mode response accordingly. In addition, all vehicles have limitations with regard to wading, and therefore it would be desirable to obtain sufficient information regarding water conditions ahead of a vehicle to enable a determination of whether it is advisable to enter the water. The known systems described above have no provision for taking such measurements for assisting driver judgement.
Against this background, it would be desirable to provide an improved water detection system for a vehicle, which overcomes or at least substantially alleviates the disadvantages known in the prior art.